As semiconductor element or magnetic head element has become smaller and more compact, the element is now structured by laminated thin films of several NMs (nanometers) within a micro region of submicrons. Since the performance of the semiconductor element or magnetic head element depends upon the structure, element distribution and crystal structure of the micro region, analysis of the micro region is very important.
For observation of the micro region, there are available a scanning electron microscope (SEM), transmission electron microscope (TEM), and scanning transmission electron microscope (STEM). TEM is an apparatus in which electron beams are irradiated onto a specimen nearly in parallel and the transmitted electron beams are magnified by a lens. STEM is an apparatus in which electron beams are converged into a micro region and, while the electron beams are scanned over a specimen two-dimensionally, the intensity of the transmitted electron beams is measured so as to acquire a two-dimensional image.
The intensity of a transmitted electron detected by a TEM and STEM correlates to the average atomic number of a portion through which the electron beam has transmitted. Because of this, thin films of chrome (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni) and copper (Cu), having an atomic number closer to each other, or silicon oxide film and silicone nitride film, having an average atomic number closer to each other, cannot be distinguished from each other.
In case of a metallic film, Cr, Mn, Fe, Co, Ni and Cu can be distinguished from each other by acquiring a two-dimensional image with the aid of fluorescent X-ray analysis. However, longer measuring time is required in obtaining the two-dimensional image because detectable fluorescent X-ray intensity is very weak. Since the fluorescent X-ray analysis is not suitable for analysis of light element, distinction of silicon oxide film from silicone nitride film is difficult.
As an analytical method for solving the above problems, there is available the electron energy loss spectroscopy (EELS) that analyzes energy of transmitted electron using an electron spectrometer. Because an electron, when it transmits through a specimen, causes energy loss peculiar to the structural element (electron structure) of the specimen, generating a two-dimensional image from the electrons after energy loss peculiar to the element makes it possible to distinguish between silicon oxide film and nitride film, which is not feasible on a TEM or STEM image. The above has been widely employed as a combined method of a STEM and a parallel-detection type electron energy loss spectrometer (EELS).
EELS has a fan-shaped magnetic field sector as an electron spectrometer, and is equipped with a quadruple electromagnetic lens before it and a sextuple electromagnetic lens after it, and a parallel detector at the most downstream. The sextuple electromagnetic lens is utilized to adjust the focus of an EELS spectrum and magnify the EELS spectrum. The quadruple electromagnetic lens is utilized to reduce the aberration of the EELS spectrum projected on the detector. The EELS spectrum magnified by the quadruple electromagnetic lens is projected on the parallel detector and electron energy loss spectra are measured in a wide range.
Prior arts relating to the structure of EELS include, for example, U.S. Pat. No. 4,743,756, Japanese Application Patent Laid-Open Publication Nos. HEI 7-21966 (1995), HEI 7-21967 (1995), and HEI 7-29544 (1995). The Laid-Open Publication No. SHO 57-80649 (1982) describes about an electron beam energy analyzer.